1 Answer
1

./<scriptname> executes <scriptname> in a child process and waits for it to exit.

. <scriptname> executes <scriptname> in the same process; the reasons this is used are usually to allow <scriptname> to modify the environment, and to perform additional actions without the resource cost of spawning a new process.

bash <scriptname> tells bash to run <scriptname>. If <scriptname> has a shebang with the path to bash (#!/bin/bash) at the top, it will have the same effect as just executing <scriptname>. If <scriptname> points to another interpreter (#!/bin/sh), then <scriptname> would normally be interpreted by that program, but you are overriding that by asking bash to interpret it.